The field of this invention is flexible shaft constructions employed to transmit rotational energy between a motor and the rotor of a centrifuge.
As the rotor of a centrifuge approaches a desired rotational speed, the shaft connecting the rotor to the motor usually passes through a phase known as the "critical speed" at which speed significant vibrations are encountered. As is apparent, it is desirable to provide centrifuges wherein vibrations are minimized to minimize the load on the motor bearings and to minimize the deleterious effects produced on a sample being centrifuged by such vibrations.
The speed at which significant amounts of vibration occur on a rotating centrifuge depends largely upon the geometry of the shaft as well as its elastic characteristics. For example, relatively stiff or thick short shafts encounter much more severe vibrations than do flexible or relatively long thin shafts. For this reason, it is advantageous to utilize flexible, relatively thin, long shafts as a means for translating the rotational energy of a motor shaft to the rotor of a centrifuge.
The foregoing construction is commonly included in centrifuges to be utilized for separating blood, because in blood separation, vibrational factors must be minimized. Unfortunately, however, a flexible shaft with a long, thin configuration is damaged easily, particularly while loading the centrifuge rotor with samples. To reduce the likelihood of such damage from occurring during the loading of the centrifuge rotor, it has been proposed that the rotating shaft be encased with a flexible material structured so that the flexible material contacts ball bearings which in turn contact a flexible race attached to a stationary housing. This construction is exemplified by the disclosure in U.S. Pat. No. 2,827,229. While the coupling remains flexible in the foregoing construction, this construction has two serious drawbacks. First, it is very expensive to produce because of the high precision with which a large number of parts must be assembled. Secondly, the bearings, within which the shaft rotates tend to confine the shaft, thereby reducing its flexibility and thereby increasing the vibration the shaft experiences while rotating at the critical speed.
Dampening means have also been proposed in order to reduce the vibrations encountered at the critical speed. For the most part, however, dampening means have proven unsatisfactory for reducing the overall vibrational effects on the samples in the centrifuge rotor.
In copending U.S. patent application Ser. No. 201,069 filed Nov. 22, 1971, by Ivan L. Lehman entitled "Flexible Shaft Stabilizer," the teachings of which are incorporated herein by reference, a construction is disclosed in which a flexible shaft is surrounded by a sleeve made from a resilient material such as natural or synthetic rubber. The resilient sleeve is enclosed by a tubular member fabricated of a non-resilient, structurally strong material, such as metal. Although the foregoing shaft construction provides improved results over prior art shaft construction in that the amount of vibration experienced by a rotor which is connected to a motor with this construction is reduced, that construction does not provide a completely satisfactory means for preventing the permanent deformation of the flexible shaft by an operator when loading and unloading the rotor.